Passive Device Designed to Facilitate Demise of A Space System During Re-Entry Into the Earth&#39;s Atmosphere

ABSTRACT

Space system comprising a structure formed by structure components, an on-board equipment carried by the structure, and a passive device designed to facilitate demise of the space system during re-entry into the Earth&#39;s atmosphere. The passive device comprises connecting members designed to stably connect the structure components. The connecting members comprise at least a portion made of a primer material with characteristics such as to decay at re-entry altitudes higher than those at which the current connecting members melt so as to make unstable the connection created by the connecting members to such an extent as to early triggering demise of the structure of the space system during re-entry into the Earth&#39;s atmosphere.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to space systems, and moreparticularly to passive devices designed to facilitate demise of spacesystems during re-entry into the Earth's atmosphere.

In particular, the present invention finds advantageous, but notexclusive, application to satellites, especially Low Earth Orbit (LEO)satellites, to which the following description will explicit referwithout thereby losing generality.

STATE OF THE ART

The impact of space activities on the space environment and on the Earthare the focus of current research. In particular, the mitigation of theimpacts on the population caused by re-entry into the Earth's atmosphereof space systems poses a number of challenges, and requires indicationson how this problem can be handled.

In fact, Earth orbit satellites, and LEO satellites, due to equipmentfailure, unexpected effects or natural orbital decay, fall on the Earthat very high speeds, thus undergoing a fragmentation caused by hightemperatures generated by the friction with the Earth's atmospherecombined with high aerodynamic forces.

The main part of the fragments dissolve in the Earth's atmosphere due tothe high friction temperatures. However, those parts made with moreheat-resistant materials are the fragments with the highest probabilityof reaching the Earth's surface.

To mitigate the risk for the population on the ground to be hit bysatellite fragments, the space agencies are imposing the implementationof a specific design parameter, called re-entry casualty risk, to lessthan 10 ⁻⁴.

Taking into account the risk for the population on the ground, thespacecraft must be designed so that those parts of the satellite whichsurvive the re-entry into the atmosphere at the end of the mission cangenerate a casualty risk lower than 10 ⁻⁴. This can be achieved throughthe careful selection of the materials and of the architecture of thespacecraft. However, these solutions must not jeopardize the spacecraftability to survive in space for a certain number of years, during whichit is subject to degradation and to the risks arising from the orbitalenvironment and from possible impacts with space debris.

The design solutions presently adopted to meet (at least partially)these conditions can be grouped into two categories.

The category normally referred to as “controlled re-entry” requireslarger propellant tanks and more robust control systems of thespacecraft holding, so as to guide the re-entering spacecraft towards anarea with low population density, for example oceans. This category,however, may be impractical in the event of an unrecoverable failure ofthe control system or of the communication system of the space system.

A category with a reduced casualty risk alternative to the controlledre-entry involves replacement of the components that can reach theEarth's surface, such as propellant tanks, with others dissolving duringthe atmospheric re-entry. This category, however, requires the use ofcomponents which are not available on the market yet.

All the aforesaid solutions, however, involve additional costs for thedesign development of the space vehicles and for the use of specialcomponents. This additional cost is not related to the spacecraftmission, but only to its re-entry.

WO 2014/045078 A1 describes a space system provided with a re-entrysignalling apparatus adapted to transmit, during re-entry of the spacesystem into the Earth's atmosphere, an alert signal containinginformation of the location, on the ground or in space, where the debrisof the space system may fall. The apparatus comprises an aerodynamiccasing provided with a thermal shield containing a geo-locationreceiver, a transmitter and a processor, and connected to the spacesystem via a connector comprising bolts which melt or become brittle ata given temperature during re-entry into the Earth's atmosphere, so asto break during the re-entry of the space system into the Earth'satmosphere and cause the casing to be released.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is therefore providing a simple andeconomical solution for the design of satellites which is able tosatisfy at the same time the requirements relating to their survival inorbit and those relating to their demise during re-entry into theEarth's atmosphere at the end of their mission.

According to the present invention, a space system is provided, asclaimed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 show a satellite in a fully assembled configuration and indifferent configurations with disassembled or removed parts to allow thevision of its interior;

FIGS. 4 to 6 show a connecting member intended to connect two satellitepanels according to an embodiment of the invention;

FIGS. 7 to 9 show a connecting member intended to connect two satellitepanels according to a different embodiment of the invention;

FIGS. 10 and 11 show a connecting member intended to connect twosatellite panels according to a further different embodiment of theinvention; and

FIGS. 12 to 14 show a connecting member intended to connect twosatellite panels according to a yet further different embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will now be described in detail with reference tothe accompanying drawings to enable a skilled person to implement anduse it. Various modifications to the embodiments described will beimmediately appreciable to the skilled person and the generic principlesdescribed may be applied to other embodiments and applications withoutthereby departing from the scope of the present invention, as defined bythe appended claims. Therefore, the present invention should not beconsidered as limited to the described and shown embodiments, but it isto be accorded the widest scope complying with the principles andfeatures described and claimed.

The present invention stems from the appreciation that satelliteon-board equipment (e.g. electronics boxes, fluidic components, tanks,etc.) is mounted to a lesser extent outside the satellite structure, forexample the antennas and the solar panels, and to a greater extentinside the satellite structure.

During re-entry into the Earth's atmosphere, aero-thermo-dynamic forcesstart to fragment the exterior equipment. The interior equipment, on theother hand, begins to fragment only after the erosion of the protectiveelements of the satellite structure. A retarding effect of thefragmentation is therefore induced by the satellite structure.

The Applicant has now conceived that, by anticipating the fragmentationof the satellite structure, also the fragmentation of the satellite isadvanced, thus increasing the exposure of the satellite fragments tohigh temperatures, with benefit to the casualty risk.

In broad terms, therefore, the present invention provides for includingin the mechanical design of the satellite a passive device designed tofacilitate the demise of the space system during re-entry into theEarth's atmosphere, and in particular formed by specific elementscapable of “triggering” in advance the demise of the satellite structureduring re-entry into the atmosphere.

The “primer” is realized by using materials able to “decay” attemperatures lower than those of the materials normally used in thesatellite structures (AL alloys, Titanium, CRFP), but at the same timesufficiently “resistant” to high temperatures and to the operatingconditions of the satellite during launch and orbit operation.

The primer elements are inserted in the mechanical mounting of thepanels to which the satellite equipment is mounted, and in particular inthe connecting members that connect the panels of the satellitestructure one to the other.

FIGS. 1 to 3 show, and indicated by 1 as a whole, a satellite designedaccording to the present invention, which should demise during re-entryinto the Earth's atmosphere at the end of its mission.

The satellite 1 essentially comprises a structure 2 formed by outer andinner panels 3 adapted to perform a structural function of support andprotection, which typically have a honeycomb structure of aluminiumalloy coated with layers of carbon fibres and are connected by means ofconnecting members 4; and an on-board equipment 5 carried by thestructure 2 of the satellite 1 and comprising an exterior equipment,such as an antenna and solar panels, carried by the outer panels, and aninterior equipment of various kinds carried by the inner panels.

According to the present invention, the satellite 1 further comprises apassive device designed to facilitate the demise of the satellite duringre-entry into the Earth's atmosphere.

The passive device is formed by the connecting members 4, which arespecially designed to stably connect the panels 3 of the structure 2 ofthe satellite 1 during launch and orbit operation of the satellite 1,and to trigger in advance the fragmentation of the structure 2 of thesatellite 1 during re-entry into the Earth's atmosphere.

To this aim, the connecting members 4 comprise at least a portion madeof a material, hereinafter referred to as “primer material”, whosecharacteristics decay at re-entry altitudes of the satellite 1 higherthan those at which the current connecting members decay, for examplebetween 120 and 70 km, so as to make unstable the connection of thepanels 3 of the structure 2 of the satellite 1 created by the connectingmembers 4 to such an extent as to trigger the demise of the structure 2of the satellite 1 during re-entry into the Earth's atmosphere inadvance with respect to what is currently occurring.

By way of non-limiting example, the primer material may convenientlycomprise a metal alloy with a low melting point comprised between 90 and120° C., and conveniently comprises an eutectic metallic.

According to a first embodiment of the invention, each connecting member4 is mounted to exert between a pair of panels 3 a stable connectionforce in a given connection direction during launch and orbit operationof the satellite 1, and to enable the two panels 3 to disengage fromeach other by sliding in a direction transverse to the couplingdirection during the satellite re-entry into the Earth's atmosphere.

A possible implementation of this first embodiment is shown in FIGS. 4to 6, wherein each connecting member 4 comprises two structural elements6, 7 made of metal, hereinafter referred to as inserts, which are stablycoupled to, in particular inserted in, the panels 3, in the exampleshown along respective edges, in a substantially intermediate position.A first insert, in the example shown the one designated by 6, isprovided with a threaded hole 8 formed on a flat face of the insert 6coplanar to the side face of the respective panel 3.

The second insert, in the example shown the one designated by 7, ishollow and defines a cavity 9 bounded by a side wall 10 and a bottom 11,which is adapted to be arranged, when the two panels 3 are connected, incontact with the face of the first insert 6 on which the threaded hole 8is formed. The bottom 11 has a slot 12 with an open side on the edge ofthe respective panel 3 which, when the two panels 3 are connected, is ina position facing the threaded hole 8 of the first insert 6.

Each connecting member 4 further comprises a screw 13, which extendsthrough the slot 12 of the second insert 7 and engages the threaded hole8 in the first insert 6 so as to exert between the two inserts 6, 7 anaxial force to keep them permanently in contact by friction and thus toprevent the radial sliding of the screw 13 with respect to the slot 12.

Each connecting member 4 further comprises a washer 14 made of saidprimer material, referred to as primer washer in the followingdescription for convenience and for distinguishing it from similarcomponents, which is inserted on the screw 13, is arranged between thescrew head and the bottom 11 and performs, among other things, thefunction of ensuring the friction and the axial reaction necessary formaintaining the connection of the two inserts 6, 7 until exceeding theoperating temperatures beyond which it liquefies, thus loosing theconnection.

Conveniently, each connecting member 4 further comprises a holedcup-shaped body 15, hereinafter referred to as holed cupel, which isinserted on the screw 13, is arranged between the primer washer 14 andthe bottom 11, and has a raised peripheral edge defining a seat in whichthe primer washer 14 is partially housed so as to protrude axially fromthe peripheral edge of the holed cupel 15. Conveniently, the raisedperipheral edge of the holed cupel 15 is so sized as to limit or preventthe radial “bulging” of the primer washer 14 under the load exerted bythe head of the screw 13, especially during the launch of the satellite1, which bulging would otherwise diminish the axial reaction of thewasher, and then the action exerted by the connecting member 4 on thetwo panels 3.

Conveniently, each connecting member 4 further comprises a furtherwasher 16, which is also inserted on the screw 13 and is arrangedbetween the head of the screw 13 and the primer washer 14 to evenlydistribute the load exerted by the head of the screw 13 on the entiresurface of the primer washer 14.

A different implementation of the first embodiment of the invention isshown in FIGS. 7 to 9, which will be described only with regard to thedifferences from the implementation shown in FIGS. 4 to 6, thereforeusing the same reference numbers to indicate the same components.

In particular, the implementation shown in FIGS. 7 to 9 differs from theone shown in FIGS. 4 to 6 in that the primer washer 14 and the holedcupel 15 are integrated in the second insert 7. To this aim, the bottom11 of the second insert 7 is provided, on its side arranged on the edgeof the respective panel 3, with an edge folded towards the inside of thecavity 9 to define, together with the bottom 11 and the side wall 10defining the cavity 9, a seat 17 wherein the primer washer 14 ispartially housed so as to protrude axially from the folded edge.

The second insert 7 thus comprises a holed plate 18 covering the primerwasher 14, said holed plate 18 having an edge folded toward the foldededge of the bottom 11 and fixed to this latter, for example by gluing,to keep the primer washer 14 in the housing 17 and prevent its radialbulging caused by the load exerted by the head of the screw 13.

In both aforesaid implementations of the first embodiment of theinvention, the aero-thermal-dynamic forces acting on the satellite 1during re-entry into the atmosphere at the end of its mission cause thealteration of the eutectic in the primer washer 14 and the consequentreduction of the coupling force exerted by the connecting members 4between the panels 3, thus allowing the second inserts 7 to slide withrespect to the corresponding first inserts 6 in directions substantiallyorthogonal to the axes of the screws 13, so that the screws 13accidentally slip out from the corresponding slots 12 causing the finaldisruption of the panels 3.

This early fragmentation of the structure 2 of the satellite 1 between120 and 70 km altitude also causes the early fragmentation of theequipment 5, thus increasing the exposure time of the fragments at hightemperatures to the benefit of the casualty risk.

In a second, different embodiment of the invention, each connectingmember 4 exerts between a pair of panels 3 a stable connection force ina given connection direction during the launch and the orbit operationof the satellite 1, thus allowing the two panels 3 to disengage fromeach other by sliding in the connection direction during re-entry of thesatellite into the Earth's atmosphere.

A possible implementation of this second embodiment is shown in FIGS. 10and 11, and will be described only with regard to its differences fromthe first embodiment shown in FIGS. 4 to 9, thus using the samereference numbers to identify the same components.

In the implementation shown in FIGS. 10 and 11, the second insert 7comprises a tubular member defining a through hole 9 which, when the twopanels 3 are connected, is coaxial to the threaded hole 8 of the firstinsert 6 and has a diameter greater than the one of the head of thescrew 13.

The primer washer 14 is arranged between the head of the screw 13 andthe through hole 9 and has an outer diameter greater than the one of thethrough hole 9 so as to extend laterally and rest on the surface of therespective panel 3, outside the through hole 9.

Conveniently, the primer washer 14 is further integrally provided with atubular appendix 14 a which is made of said primer material, extendsthrough the through hole 9 and is sized so as to completely fill thethrough hole 9.

In this implementation, the melting of the primer washer 14 and of itsappendix 14 a during re-entry of the satellite 1 into the Earth'satmosphere removes any connection between the two panels 3, allowingthem to disengage from each other by sliding in the coupling direction.

A different implementation of the second embodiment of the invention isshown in FIG. 12, which will be described only with regard to thedifferences from the implementation shown in FIGS. 10 and 11, thus usingthe same reference numbers to identify the same components.

In particular, the implementation shown in FIG. 12 differs from the oneshown in FIGS. 10 and 11 in that both panels are fitted with identicalinserts to the first insert 6 and are connected together through anL-shaped bracket 20 whose arms 20a are respectively connected to acorresponding insert 6 by means of screws 13 which engage respectiveholes made in the arms 20a via the respective primer washers 14 deprivedof the appendix 14 a.

The holes formed in the arms 20 a of the bracket 20 have a greaterdiameter than the one of the heads of the screws 13, while the primerwashers 14 have an outer diameter greater than the one of the holesformed in the arms 20 a of the bracket 20.

As shown in FIGS. 13 and 14, the inserts 6 may be of either asingle-hole type, as shown in FIG. 13, or a double-hole type, as shownin FIG. 14. In this latter case, the two panels 3 may be connectedthrough a single suitably holed L-shaped bracket, or through twoseparate L-shaped brackets of the type shown in FIG. 12.

Analogously to the implementation shown in FIGS. 10 and 11, also in theimplementation shown in FIGS. 12 to 14, the melting of the primerwashers 14 during re-entry of the satellite 1 into the Earth'satmosphere removes any connection between the two panels 3 and thebracket 20, allowing them to disengage from each other by sliding in thecoupling direction.

The various embodiments and implementations of the present inventiondescribed above and shown in the attached drawings may be modified andvaried without thereby departing from the protective scope of thepresent invention, as defined in the appended claims.

For example, the connecting members may be of a type different fromthose previously described and shown in the drawings. In particular,instead of being of the type based on a threaded engagement, which isformed by pairs of threadly engaged mating elements comprising a malethreaded element (screw 13) and a female threaded element (threaded hole6 in the insert 6), the connecting members may be of the type based onrivets or hinges.

On the basis of the aforesaid, the advantages of the present inventionwith respect to the state of the art solution are evident.

In particular, the present invention satisfies the requirements relatingto the survival in orbit of the satellites and those relating to theirdemise during the re-entry into the atmosphere at the end of the missionby means of an extremely simple and economical solution that does notrequire the redesign of other parts of the satellites.

1. A space system (1) comprising a structure (2) formed by structurecomponents (3), an on-board equipment (5) carried by the structure (2),and a passive device designed to facilitate early demise of the spacesystem (1) during re-entry into the Earth's atmosphere; the passivedevice comprises connecting members (4) designed to stably connect thestructure components (3) to each other; each connecting member (4)comprises a plurality of components (6, 7, 13, 14) designed to mate witheach other so as to create a stable connection between a correspondingpair of structure components (3) in a connection direction during launchand orbit operation of the space system (1); characterized in that atleast one primer component (14) in a connecting member (4) is made of aprimer material which is different from that of the other components (6,7, 13) and whose characteristics are such as to decay at re-entryaltitudes higher than those at which the characteristics of thematerials of the other components (6, 7, 13) decay, so as to loosen inadvance the stable connection created by the components of theconnecting member (4) during re-entry of the space system (1) into theEarth's atmosphere to such an extent as to allow the two structurecomponents (3) to disconnected from each other, thus early triggeringdemise of the structure (2) of the space system (1).
 2. A space systemaccording to claim 1, wherein at least part of the components (6, 7, 13)in each connecting member (4) are coupled by means of a threadedengagement and the primer component is in the form of a washer (14). 3.A space system according to claim 1 or 2, wherein the connecting members(4) are designed to cause the corresponding pairs of structurecomponents (3) to disengage from each other by sliding in the connectiondirection.
 4. A space system according to claim 3, wherein eachconnecting member (4) comprises two inserts (6, 7), each of which isstably coupled to a respective structure component (3); a first insert(6) is provided with a threaded hole (8), and the second insert (7)comprises a tubular member defining a through hole (9) which, when thetwo structure components (3) are connected, is coaxial to the threadedhole (8) in the first insert (6); the connecting member (4) furthercomprises a screw (13), which extends through the through hole (9) andengages the threaded hole (8); and a primer washer (14) formed in saidprimer material, inserted on the screw (13) and arranged between an headof the screw and the through hole (9) in the second insert (7), andhaving an outer diameter greater than that of the through hole (9) so asto extend laterally and rest on the surface of the relative structurecomponent (3), outside the through hole (9).
 5. A space system accordingto claim 4, wherein the primer washer (14) is further integrallyprovided with a tubular appendix (14 a), which is made of said primermaterial, extends through the through hole (9) and is sized so as tofill entirely the through hole (9).
 6. A space system according to claim3, wherein each connecting member (4) comprises two inserts (6), each ofwhich is stably coupled to a corresponding structure component (3) andis provided with a threaded hole (8); the connecting member (4) furthercomprises an L-shaped bracket (20) with arms (20 a) respectively boundto respective inserts (6) by means of screws (13) that engage respectiveholes in the arms (20 a) via respective primer washers (14) formed ofsaid primer material; the holes in the arms (20 a) of the bracket (20)have a diameter greater than the ones of the heads of the screws (13),while the primer washers (14) have an outer diameter greater than theone of the holes in the arms (20 a) of the bracket (20).
 7. A spacesystem according to claim 6, wherein the inserts (6) are of either asingle-hole type or a double-hole type.
 8. A space system accordingclaim 1 or 2, wherein the connecting members (4) are designed to allowthe respective pairs of structure components (3) to disengage from eachother by sliding in a direction transverse to the connection direction.9. A space system according to claim 8, wherein each connecting member(4) comprises two inserts (6, 7), each of which is stably coupled to arespective structure component (3) along an edge of the respectivestructure component (3); a first insert (6) is provided with a threadedhole (8), and the second insert (7) has a slot (12), which has an openside on the edge of the respective structure component (3) and isarranged, when the two structure components (3) are coupled, in aposition facing the threaded hole (8) of the first insert (6); theconnecting member (4) further comprises a screw (13) which extendsthrough the slot (12) and engages the threaded hole (8); and a primerwasher (14), which is made of said primer material, is inserted on thescrew (13) and is arranged between a head of the screw (13) head and theslot (12) in the second insert (7); whereby the decay of the primermaterial during re-entry of the space system (1) into the Earth'satmosphere results in the reduction of the connecting force exerted bythe connecting member (4) between the two structure components (3), soas to allow the second insert (7) to slide with respect to the firstinsert (6) in a direction substantially orthogonal to the axis of thescrew (13) until the screw (13) is caused to exit from the slot (12),with a consequent disengagement of the two structure components (3). 10.A space system according to claim 9, wherein each connecting member (4)further comprises a holed cupel (15) which is inserted on the screw (13)and has a raised peripheral edge defining a seat in which the primerwasher (14) is partially housed so as to axially protrude from theperipheral edge of the holed cupel (15).
 11. A space system according toclaim 9, wherein the primer washer (14) is integrated in the secondinsert (7).
 12. A space system according to claim 11, wherein the secondinsert (7) defines a cavity (9) delimited by a side wall (10) and by abottom (11), which is in contact with the first insert (6) when the twostructure components (3) are coupled, and in which the slot (12) isformed; the bottom (11) is provided, on its side arranged on the edge ofthe respective structure component (3), with an edge which folds towardsthe inside of the cavity (9) and defines, along with the bottom (11) andthe side wall (10), a housing (17) in which the primer washer (14) ispartially housed so as to axially protrude from the folded edge of thebottom (11); and wherein the second insert (7) further comprises acovering holed plate (18) to hold the primer washer (14) in the housing(17) when the screw (13) engages the threaded hole (8) of the firstinsert (7).
 13. Use of a passive device having the features claimed inclaim 1 in a space system (1) to facilitate demise of the space system(1) during re-entry into the Earth's atmosphere.